Method of making silver thiosulphate



Patented Oct. 10, 1933 e 7 1 929 4 UNITED-STATES: PATENT OFFICE METHOD OF MAKING SILVER THIOSULPHATE James J. Bajda, South Orange, N. J.

No Drawingj Application March 27, 1929 Serial No. 350,453

7 8 Claims. (01. 23-115) The production of silver sodium thiosulphate drained or filteredprecipitate of silver chloride; has been accomplished by evaporating a solution If the latter sequence of steps be employed it of silver chloride in the presence of sodium thio is preferable to add only a portion, say fifty sulphate, or by adding a solution of silver nitrate per cent, of the requisite amount of molten soto a solution of sodium thiosulphate to produce dium thiosulphate to the silver chloride, and, 0

a precipitate which is made available by the after thorough agitation, add the remainder of addition of ethyl alcohol and subsequent filtering. the molten sodium thiosulphate.

These processes or processes of similar nature Adding a quantity of common salt, after the are uneconomical and unsatisfactory for comcomplete dissolution of the silver chloride, may 10 mercial use because of the difiiculty of separatrv if n cess ry, to a ist ill-completing the 65 ing the resultant silver thiosulphate, which is precipitation of the silver sodium thiosulphate, soluble in water to a marked degree, is unstable, which then as previously explained may be filand possesses a marked tendency to decompose tered or drained off and dried. at high temperatures; and for other reasons that Whether the molten sodium thiosulphate be need not be gone into. added to the silver chloride, or the reverse order 70 I have found, however, that alkali silver thiobe followed, advantages may be gained by carry sulphate, in a state suiiiciently pure for pracing out the reaction in a special reaction vessel tical purposes, may be economically obtained by such as a ball mill, the operation of which tends a reaction between reagents one or more of which to produce the complete comminution of any has been melted: preferably a reaction between lingering particles of silver chloride that might 75 silver chloride and sodium thiosulphate which otherwise remain uncombined.v has been heated and thereby melted with little, Regarding formula showing the reaction and if any, addition of water besides its own water the end products, itis difiicult to write a single of crystallization. formula because the indications are that the Having thus melted the desired quantity of reaction proceeds in a variety of ways and forms so sodium thiosulphate crystals, the silver chloride .various silver thiosulphates. For example, when 1 may be added thereto, whereupon, depending silver chloride (AgGl) reacts with molten sodium upon the degree of heat employed above the thiosulphate (NazS2O35l-I2O), the silver of the melting point (48 to 49 C.) of the thiosulphate, silver chloride displaces in whole or in part the arapid reaction takes place wherein the resultant sodium of the sodium thiosulphate with result- '85,

silver sodium thiosulphate is produced in relaing formation of silver thiosulphate and sodium tively P y ta in o With ut d D Sichloride. Then the silver thiosulphate combines tiOn, and y be readily Separated from the in varying proportions with other molecules of 6. ct a y filtering draining Saidsodium thiosulphate which crystallize out or pre-' ystalli e product therefrom. It m then be cipitate as a double salt having a greater or less dried at elevated temperatures Without mechem' number or" molecules of water of crystallization cal or chemical loss due to decomposition or other combined therewith However, analytical t eausesindicate that the predominant silver thiosul- The use Of a water bath has been found by phat-, producedby my foregoing process has sub..

40 me to be acceptable in melting the crystalline Stan/many the f l Ag2S2O32Na2s2Q321-12Q sodium thiosulphate in preparation for its use I Claim;

in the above reeetien- 1. The process of making a silver thiosulphate And I have also found Well to use silver product which comprises causing a reaction beehleride which has been freshly precipitated, and tween silver chloride and sodium thiosulphate in 5 before using it to wash it free from soluble ima molten t t 0 pu iti s by t us of wat f m whi it may 2. The process of making a silver thiosulphate be separated either by decantation or filtration. product which comprises causing a reaction be- The d p Silver Chloride y be dua y tween a suitable silver salt'and an alkali-thiobut reasonably rapidly added to the completely sul hate in a molten state.

' 5O molten sodium thiosulphate, the temperature of 3. The process of making a silver thiosulphate 10 which should not exceed ninety-five to one huhproduct which comprises causing a reaction bedred degrees centigrade; although if circumtween a suitable silver salt and a sodium thiosulstances render it desirable the reaction may be phate in a molten state to form a silver thiosulcarried out with satisfactory results by adding phate product, cooling the reaction mass to cryslihe molten Sodium phate to the well tallize out the product, and mechanically sepa able silver salt and molten sodium thiosulphate to a temperature, between the melting point of the thiosulphate and below about 95 C., suitable for forming the silver thiosulphate product, cooling the reaction mass to crystallize out the product, and mechanically separating it from the remainder of the reaction mass.

6. The process of making a silver thiosulphate product which comprises comminuting and agitating' together a suitable silver salt and molten sodium thiosulphate heated to a temperature,

between the melting point of the thiosulphate and below about 95 0., suitable for forming a silver thiosulphate product.

'7. The process of making a silver thiosulphate product which comprises heating together a suitable silver salt and an alkali thiosulphate in a molten state until the silver salt is substantially completely dissolved, cooling the reaction mass to crystallize out the product, and adding a suitable quantity of common salt to the reaction mass to render more complete said crystallization.

8. The process of making a silver thiosulphate product, which consists in causing a reaction to take place between silver chloride and an alkalithiosulphate in a molten state, the silver chloride having first been washed substantially free of soluble impurities.

JAMES J. BAJDA. 

